1. Field of Invention
The invention relates to a method and device for producing and filling sacks. The material that forms the sacks is supplied in the form of a tubular material from an unwinding device to a sack-forming device. The tubular material is separated into individual tube pieces in the sack-forming device and the tube pieces are transported by grippers during at least one part of their path in the sack-forming device.
2. Description of the Prior Art
Sacks are produced inter alia by so-called “Form, Fill and Seal” machines (referred to as FFS machines in the following).
These machines, which are shown inter alia in the patent specifications DE 199 33 486, EP 534 062, DE 44 23 964, DE 199 20 478 and DE 199 36 660, have unwinding devices, on which tubes are stored. The tube is unwound by these unwinding devices and separated into tube pieces. Usually, tube bottoms are formed, filling material is filled in the resulting sack and the sack is sealed in the additional work steps. The type of sack formation and filling shown in the afore-mentioned documents forms a part of the contents disclosed in this document. The same applies to the definitions of the term “Form, Fill and Seal” machines (FFS) provided in these documents and also to the transport of the film tubes, film sections and sacks into these machines. Usually bulk materials are filled using these machines.
As a rule, for the purpose of processing on the FFS machines, film tubes are formed by blown film extrusion, the format of the film tubes (here their circumference) corresponding to that of the formed sack. However, as a result of this approach, it is necessary to carry out expensive format changes at the extrusion systems with relative frequency in order to be able to realize different sack formats. Furthermore, the formats required for the sack formation, are relatively small and can be produced in a relatively uneconomic manner. Blown film extrusion systems of a larger format produce the same film at lower costs per unit of area.
Therefore, many a time attempts are made to produce initially very broad film webs by flat film extrusion or by blown film extrusion on systems of a large format, wherein usually blown film extrusion systems were preferred likewise primarily for reasons of economy. The resulting film tubes or film webs of large format were then processed further into flat film webs by cutting them in accordance with the format.
Subsequently, one of these laid flat film webs was folded together into a tube and joined by a longitudinal weld seam to form a tube. However, the use of the machines described is primarily limited to industrial applications, such as the bagging of dyes, plastic granulate, fertilizers and other bulk materials.
Consumer goods sold by retail are usually transported and distributed in sacks of a higher quality. It is thus known, for example, to produce side-gusseted bags or side-gusseted sacks from tube pieces, which are formed from several film sections. The edges of the respective film sections are usually heat-sealed to one another for this purpose. This procedure is carried out between welding jaws, which arrest the material to be heat-sealed during the welding process.
Tube pieces are usually produced in this way, the length of which corresponds to that of the sacks formed subsequently. In other cases, directly after production, the tube pieces formed are provided with the length of the sack formed subsequently and supplied individually to the sack-forming and filling devices. This type of forming high-quality sacks is well known, for example, in the field of pet foods. Here, emphasis is laid on side-gusseted sacks, which have edge seams on each of their outer folds. These sacks are rumored to have greater stability and a better appearance, in particular. These sacks are usually produced by initially producing a tube by the longitudinal welding of a flat film. This tube is separated into individual tube pieces and is provided with additional longitudinal weld seams.
However, both the transport of the individual tube pieces and the subsequent introduction of the latter into a sack-forming and filling process are complex. This usually takes place using rotary feeders or other suction devices, which grasp the tube pieces individually and supply them to the sack-forming device. Such suction devices are expensive and prone to faults.